NO. 9 GRAND CANYON FOSSIL FOOTPRINTS GILMORE II 



imprints of the feet, must have been about equally distributed between 

 the fore and hind limbs. 



The series of tracks selected as the type of the new species 

 Nanopus merriami are of especial interest from the fact that they 

 mark the lowest horizon in the Coconino sandstone where fossil foot- 

 prints were found in situ. This level is about 20 feet above the base 

 of the Coconino sandstone, or about 1,080 feet below the rim of the 

 canyon. Only the obverse of the foot impressions was secured (see 

 pi. 4, fig. 2), but a plaster cast shows the imprints as clearly as they 

 were on the original rock surface. 



The presence of three and four digits respectively on the manus 

 and pes; parallel grouping of the two middle toes of the hindfoot, 

 which .are subequal in length ; forefoot placed in front of the 



Fig. 6. — Nanopus caudatus Marsh. Outline of left fore and hind 

 footprints. Natural size. (After Marsh.) 



hind; broadly rounded sole; and small size (see fig. 5) constitute 

 a group of characters found in the genus Nanopus^ from the Coal 

 Measures of Kansas (fig. 6), a genus with which the present species 

 seems to have its closest affinities. The genus Barillopus established 

 by Matthew ^ upon footprints from the Coal Measures of Nova Scotia 

 has a similar digital formula (see fig. 7) but the subequal length 

 and parallel grouping of the three outer digits of the pes, the widely 

 divergent toes of the manus, and the placing of the hindfoot upon the 

 track of the fore, seem sufficient to show the distinctness of Baril- 

 lopus from the footprints under consideration. The slenderness 

 of the digits terminated with sharp claws in Barillopus are, however, 

 more in accord with the present specimen than the heavy toes with 

 rounded extremities without claws in the type of the genus Nanopus. 



* Marsh, O. C, Amer. Journ. Sci., Vol. 48. 1894, p. 82, pi. 2, fig. i, pi. 3, fig. i. 

 ' Matthew, G. F., Canadian Rec. Sci., Vol. 9, No. 2, 1903, p. 103. 



